source: vendor/bash/3.1-p17/examples/scripts.v2/rename

#! /bin/bash
#
# original from:
# @(#) rename.ksh 1.1 94/05/10
# 90/06/01 John DuBois (spcecdt@armory.com)
# 91/02/25 Improved help info
# 92/06/07 remove quotes from around shell pattern as required by new ksh
# 94/05/10 Exit if no globbing chars given.
#
# conversion to bash v2 syntax by Chet Ramey

phelp()
{
echo "$usage
All files that match oldpattern will be renamed with the
filename components that match the constant parts of oldpattern
changed to the corresponding constant parts of newpattern.
The components of the filename that match variable parts of
oldpattern will be preserved.  Variable parts in oldpattern
must occur in the same order in newpattern.  Variables parts
can be '?' and '*'.
Example: 
rename \"/tmp/foo*.ba.?\" \"/tmp/new*x?\"
All files in /tmp that match foo*.ba.? will have the \"foo\" part
replaced by \"new\" and the \".ba.\" part replaced by \"x\"."
}

usage="usage: $name [-htv] oldpattern newpattern"
name=${0##/}

while getopts "htv" opt; do
    case "$opt" in
    t) tell=true;;
    v) verbose=true;;
    h) phelp; exit 0;;
    *) echo "$name: $usage" 1>&2; exit 2;;
    esac
done
shift $((OPTIND - 1))

if [ $# -lt 2 ]; then
    phelp
    exit 2
fi

oldpat=$1
newpat=$2

set -- $1
if [ ! -e "$1" ]; then
    echo "$name: no files match $oldpat."
    exit 1
fi

typeset -i i=1 j

# Example oldpat: foo*.a
# Example newpat: bar*.b

# Examples given for first iteration (in the example, the only interation)
while :; do
    case "$oldpat" in
    *[\*\?]*)   ;;
    *)          break;;
    esac

    # Get leftmost globbing pattern in oldpat
    pat=${oldpat#*[\*\?]}       # pat=.a
    pat=${oldpat%%"$pat"}       # pat=foo*
    pat=${pat##*[!\?\*]}        # pat=*
    # Find parts before & after pattern
    oldpre[i]=${oldpat%%"$pat"*}        # oldpre[1]=foo
    oldsuf[i]=${oldpat#*"$pat"}         # oldsuf[1]=.a
    newpre[i]=${newpat%%"$pat"*}        # newpre[1]=bar
    # Get rid of processed part of patterns
    oldpat=${oldpat#${oldpre[i]}"$pat"} # oldpat=.a
    newpat=${newpat#${newpre[i]}"$pat"} # newpat=.b
    let i=i+1
done

if [ $i -eq 1 ]; then
    echo "No globbing chars in pattern." 1>&2
    exit 1
fi

oldpre[i]=${oldpat%%"$pat"*}    # oldpre[2]=.a
oldsuf[i]=${oldpat#*"$pat"}     # oldsuf[2]=.a
newpre[i]=${newpat%%"$pat"*}    # newpre[2]=.b

if [ -n "$verbose" ]; then
    j=1
    while let "j < i"; do
        echo \
"Old prefix: ${oldpre[j]}   Old suffix: ${oldsuf[j]}   New prefix: ${newpre[j]}"
        let j=j+1
    done
fi

# Example file: foox.a

for file; do
    j=1
    origname=$file      # origname=foox.a
    newfile=
    while let "j <= i"; do
        # Peel off a prefix     interation      1               2
        file=${file#${oldpre[j]}}               # file=x.a      file=
        # Save the part of this prefix that is to be retained
        const=${file%${oldsuf[j]}}              # const=x       const=
        newfile=$newfile${newpre[j]}$const      # newfile=barx  newfile=barx.b
        file=${file#$const}                     # file=.a       file=.a
        let j=j+1
    done
    if [ -n "$tell" ]; then
        echo "Would move \"$origname\" to \"$newfile\"."
    else
        if [ -n "$verbose" ]; then
            echo "Moving \"$origname\" to \"$newfile\"."
        fi
        mv $origname $newfile
    fi
done